In order to measure the content of gas inhaled and exhaled by a patient utilizing a respirator, a monitoring device is often connected to the gas lines extending between the patient and the respirator in contact with the gases directed to and expired from the patient. To measure the volume and/or mass of the gas passing between the patient and the respirator, the monitoring device includes a sensor disposed within the path of the flowing gas in order to provide data on the gas flow that can be utilized to quantitatively determine the amount (volume and/or mass) of gas inhaled and/or exhaled by the patient.
For most sensors of this type, the gas flow is passed through a tube section of the sensor incorporating a type of restriction, and preferably a venturi, which creates a pressure drop between the inlet for the gas flow and the outlet for the gas flow from the tube section when the gas is flowing in either direction. This pressure difference is ascertained by a measuring device which senses the pressures at the gas flow inlet and gas flow outlet of the restriction in order to determine a corresponding flow rate for the gas flow which can then be used to determine the volumetric and/or mass flow rate of the gas.
However, based on the configuration of the restriction in the tube sections, in certain applications the measuring device is not capable of accurately determining the pressure differential within the tube section. More particularly, with regard to neonatal applications, due to the small volume of gas flowing into and out of the patient, with certain tube section designs the gas flow may pass completely through the center of the tube section without contacting the restriction. By not contacting the restriction, there is no consequent measurable pressure drop in the gas flow across the restriction. As a result, it is impossible for the measuring device to determine a volumetric and/or mass flow rate of the gas flowing through the tube section in order to effectively monitor the patient.
Therefore, it is desirable to develop a respirator sensor with a the tube section that is capable of directing the flow of gas through the tube section in a manner which ensures that the gas flow will contact the restriction present in the tube section, regardless of the size of the flow of gas. As a result, the tube section creates an effective pressure drop across the restriction within the section that can be measured by the measuring device to provide an accurate measurement of the volumetric or mass flow rate of the gas inhaled and exhaled by the patient. Further, it is desirable to form a device for this purpose that can be incorporated into original tube section constructions or can be used to retrofit existing tube sections in order to reduce the time and expense of forming tube sections with the device that is suitable for neonatal use.